1. Technical Field
The present invention relates to an electric power steering controller and a control method, and more particularly to an electric power steering controller and a control method for an automotive vehicle to aid a steering force of a driver by generating an assistant torque in a steering system.
2. Background Art
In an example, Japanese laid open Patent No. 7-186994, in FIG. 13 shows a configuration of an electric power steering controller. In this figure a steering torque detector 1 detects a steering torque of a driver. A steering torque control unit 2 computes an auxiliary torque based on an output of the steering torque detector 1. A motor speed detector 3 detects a speed of a motor. A damping compensator 4 computes a damping compensating signal based on the speed of the motor detected by the motor speed detector 3. A motor acceleration detector 5 detects a acceleration of a motor using an output of the motor speed detector 3. An inertia compensator 6 computes an inertia compensating signal based on the acceleration of the motor detected by the motor acceleration detector 5. A judging unit 7 judges whether a direction of an output of the steering torque detector 1 and an output of the motor speed detector 3 are identical, and outputs the judgment result to the steering torque control unit 2, the damping compensator 4, and the inertia compensator 6. A first adder 8 adds the auxiliary torque signal, the damping compensating signal, and the inertia compensating signal. A motor current determiner 9 computes an aimed, i.e., target, current signal from an aimed torque, which is equal to an output of the first adder 8. A motor 10 drives a steering mechanism by generating an auxiliary torque approximately proportional to a motor current, which is generated according to an applied voltage. A motor current detector 11 detects a current of the motor 10. A second adder 12 computes a difference between the aimed current signal, which is the output of the motor current determiner 9, and the current of the motor detected by the motor current detector 11. A motor driver 13 determines and applies a voltage to the motor 10 based on an error signal between the aimed current signal computed by the motor current determiner 9 and the current of the motor detected by the motor current detector 11. A vehicle speed detector 14 detects a speed of the vehicle, and outputs the speed of the vehicle detected to the steering torque controller 2, the damping compensator 4, and the inertia compensator 6.
When a driver handles a steering wheel, the steering torque is measured by the steering torque detector 1, and is output to the steering torque controller 2. The steering torque controller 2 computes an auxiliary torque signal approximately proportional to the output signal of the steering torque detector 1, and assists the steering torque of the driver by controlling the motor 10 based on the auxiliary torque signal.
At this time, the judging unit 7 judges whether the direction of an output of the steering torque detector 1 and that of the motor speed detector 3 are same or not, and if the directions are same, both the damping compensator 4 and the inertia compensator 6 are stopped and only the torque controller 2 is operated. The steering torque controller 2 determines the auxiliary torque signal according to the output of the steering torque detector 1 and the speed signal from the vehicle of the vehicle speed detector 14. The aimed torque is determined based on the auxiliary torque signal, and a motor driving current is determined by the motor current determiner 9.
When the directions mentioned above are different, the steering torque controller 2 is stopped, and both the damping compensator 4 and the inertia compensator 6 are operated. The aimed torque is determined based on the outputs of the damping compensator 4 and the inertia compensator 6, and the motor driving current is determined by the motor current determiner 9. In this case, the direction of the aimed torque is made to coincide with a direction of a motor rotation when the vehicle speed is low, and, similarly, the direction of the aimed torque is made to oppose the direction of the motor rotation when the vehicle speed is high. Therefore, when a driver is handling the steering wheel in the direction for the steering angle to increase, the steering torque required by the driver is assisted to mitigate the steering torque required. Moreover, the motor 10 is also controlled in the following fashion. When a driver is turning the steering wheel in the direction for the steering angle to decrease, he is assisted in returning the steering wheel to its original position when the vehicle speed is low, and is also assisted to prevent the steering wheel from returning excessively when the vehicle speed is high.
In general, a driver turns the steering wheel at a curve or a crossing of a road, and then returns the steering wheel, for returning to straight running making use of a voluntary return force from the road surface reaction torque of a tire. However, there are frequently cases, wherein the road surface reaction torque of the tires is small enough to cause the road surface reaction torque to become smaller than a friction torque in the steering mechanism, and the steering wheel does not return to a straight path when the vehicle speed is low or steering operation is minute. Therefore, in this case, a driver himself has to return the steering wheel by adding steering torque, hence there is a problem that the steering feeling is reduced.
Regarding this point in the prior art, the output of the steering torque detector 1 and the output of the motor speed detector 3 are checked for their coincidence, and if the result is different, the return ability of the steering wheel is raised by determining the motor driving current so that the motor 10 is rotated in the same direction as the rotating motor.
As heretofore explained, in the prior art the steering wheel is in a halted condition and the motor 10 does not rotate unless a driver applies a steering torque to the steering wheel into a returning direction when the steering wheel is handled in a range of the small road surface reaction torque of the tier in case the vehicle is curving a crossing at a low speed or running along a loose curve at a high speed. In this case the judging unit 7 is unable to judge whether or not the direction of the output of the steering torque detector 1 and that of the motor speed detector 3 is identical. Accordingly, there is a problem, wherein the motor driving current can not be determined so as to drive the motor 10 into the same direction with the rotating motor, hence the returnable ability of the steering wheel can not be raised. There is also another problem, wherein a running becomes difficult in a bad condition like a slippery snowy road as no control according to the road surface condition is executed.
In view of the above, it is the object of the present invention to provide an electric power steering controller and a control method for an automotive vehicle capable of promoting a returnable ability of a steering wheel under the various driving conditions, wherein the steering wheel is returnable without a torque being applied by a driver into a returning direction , and instead a returning control of the steering wheel is executed depending on a steering angle at will of the driver even in a running condition such that a vehicle is turning a crossing at a low speed or curving along a road at a high speed.
Furthermore, it is another object of the present invention to provide a control method of the electric power steering controller to attain the above object.
According to this invention ,an electric power steering controller for an automotive vehicle to assist a steering torque of a driver to a steering wheel comprising:
a motor for generating an assistant torque to assist said steering torque of a driver,
a steering torque detecting means for detecting the steering torque of a driver,
a steering angle detecting means for detecting a steering angle of said steering wheel,
a first reaction torque estimating means for estimating a first road surface reaction torque using said steering torque detected by said steering torque detecting means,
a second reaction torque estimating means for estimating a second road surface reaction torque using said steering angle detected by said steering angle detecting means,
a return torque compensating means for computing a first auxiliary return torque signal to control said assistant torque of said motor depending on said first road surface reaction torque estimated by said first reaction torque estimating means, and for computing a second auxiliary return torque signal to control said assistant torque of said motor depending on said second road surface reaction torque estimated by said second reaction torque estimating means,
wherein said return torque compensating means controls said assistant torque of said motor into the direction for said steering wheel to return to its original position by using both said first and said second auxiliary return torque signals.
In the above steering cotroller, said return torquecompensating means multiplies said second road surface reaction torque estimated by said second reaction torque estimating means by a gain constant, and then limits the maximum value of the above multiplied signal for computing said second auxiliary torque signal.
Furthermore, in the electric power steering controller said return torque compensating means multiplies said road surface reaction torque detected by said reaction torque estimating means by a gain constant, and then computes said first auxiliary return torque signal by limiting a maximum value of the multiplied signal with a limiter.
Furthermore, in the electric power steering controller said return torque compensating means controls said assistant torque of said motor by multiplying said first and said second auxiliary return torque signals by a weight coefficient in a weighting.
Furthermore, in the electric power steering controller said weighting made by said return torque compensating means is carried out based on at least one signal of a vehicle speed signal and a bank angle signal on a road surface.
Furthermore, in the electric power steering controller said weight coefficient used in weighting is set based on a comparison between said first and said second road surface reaction torques.
Furthermore, in the electric power steering controller said weight coefficient is set based on a difference of said first and said second road surface reaction torques.
Furthermore, in the electric power steering controller said weight coefficient is set based on a ratio of said first and said second road surface reaction torques.
Furthermore, in the electric power steering controller further comprising a road surface condition judging means for judging a road surface condition using said first and said second road surface reaction torques.
Furthermore, in the electric power steering controller said road surface condition judging means compares an absolute value of said first road surface reaction torque with that of said second road surface reaction torque, and judges a road surface condition to be a non-high friction road if said absolute value of said second road surface reaction torque is larger than that of said first road surface reaction torque, and simultaneously if a difference of said absolute values of said first and said second road surface reaction torques exceeds a predetermined value.
Furthermore, in the electric power steering controller said road surface condition judging means compares an absolute value of said first road surface reaction torque with that of said second road surface reaction torque, and judges a road surface condition to be a non-high friction road if said absolute value of said second road surface reaction torque is larger than that of said first road surface reaction torque, and simultaneously if said ratio of said absolute values of said first and said second road surface reaction torques exceeds a predetermined value.
Furthermore, in the electric power steering controller a judged result by said road surface condition judging means is used to compensate for said weight coefficient.
Furthermore, in the electric power steering controller said return torque compensating means makes said weight coefficient larger which is to be multiplied to said first auxiliary return torque signal if a road surface condition is judged to be said non-high friction road by said road surface condition judging means.
Furthermore, in the electric power steering controller said return torque compensating means controls said assistant torque of said motor based on said second auxiliary return torque signal if said road surface condition is judged to be a high friction road by said road surface condition judging means, and also controls said assistant torque of said motor by making said weight coefficient smaller which is to be multiplied to said second auxiliary return torque signal if said road condition is judged to be said non-high friction road by said road surface condition judging means.
In addition, an electric power steering controller for an automotive vehicle to assist a steering torque of a driver to a steering wheel comprising:
a motor for generating an assistant torque to assist said steering torque of a driver,
a speed detecting means for detecting a speed of the automotive vehicle,
a steering torque detecting means for detecting the steering torque of a driver,
a steering angle detecting means for detecting a steering angle of said steering wheel,
an acceleration detecting means for detecting an acceleration of said motor,
a current detecting means for detecting a current of said motor,
a first reaction torque estimating means for estimating a first road surface reaction torque obtained by letting a signal pass through a low pass filter, wherein the signal is computed from said steering torque detected by said steering torque detecting means, said acceleration of said motor detected by said acceleration detecting means, and said current of said motor detected by said current detecting means,
a second reaction torque estimating means for estimating a second road surface reaction torque using said speed of said automotive vehicle detected by said speed detecting means,
and said steering angle detected by said steering angle detecting means, and
a return torque compensating means for computing a first auxiliary return torque signal to control said assistant torque of said motor depending on said first road surface reaction torque estimated by said first reaction torque estimating means, and for computing a second auxiliary return torque signal to control said assistant torque of said motor depending on said second road surface reaction torque estimated by said second reaction torque estimating means, wherein said return torque compensating means controls said assistant torque of said motor into the direction for said steering wheel to return to its original position by using both said first and said second auxiliary return torque signals.
In addition, an electric power steering controller to assist a steering torque of a driver to a steering wheel comprising:
a motor for generating an assistant torque to assist the steering torque of a driver,
a steering torque detecting means for detecting said steering torque of a driver,
a steering angle detecting means for detecting a steering angle of said steering wheel,
a reaction torque estimating means for estimating a road, surface reaction torque using said steering torque detected by said steering torque detecting means, and
a return torque compensating means for computing a first auxiliary return torque signal to control said assistant torque of said motor depending on said road surface reaction torque estimated by said reaction torque estimating means, and for computing a second auxiliary return torque signal to control said assistant torque of said motor depending on said steering angle detected by said steering angle detecting means,
wherein said return torque compensating means controls an auxiliary torque of said motor into the direction for said steering wheel to return to its original position by using both said first and said second auxiliary return torque signals.
In addition, an electric power steering controller for an automotive vehicle to assist a steering torque of a driver to a steering wheel comprising:
a motor for generating an assistant torque to assist the steering torque of a driver,
a speed detecting means for detecting a speed of said automotive vehicle,
a steering torque detecting means for detecting the steering torque of a driver,
a steering angle detecting means for detecting a steering angle of the steering wheel,
an acceleration detecting means for detecting an acceleration of said motor,
a current detecting means for detecting a current of said motor,
a reaction torque estimating means for estimating a road surface reaction torque which is obtained by letting a signal pass through a low pass filter, wherein the signal is computed from said steering torque detected by said steering torque detecting means, said acceleration of said motor detected by said acceleration detecting means, and said current of said motor detected by said current detecting means, and
a return torque compensating means for computing a first auxiliary return torque signal to control said assistant torque of said motor depending on said road surface reaction torque estimated by said reaction torque estimating means, and for computing a second auxiliary return torque signal to control said assistant torque of said motor depending on said speed of said automotive vehicle detected by said speed detecting means and said steering angle detected by said steering angle detecting means,
wherein said return torque compensating means controls said assistant torque of said motor into the direction for said steering wheel to return to its original position by using both said first and said second auxiliary return torque signals.
In addition, an electric power steering control method for an automotive vehicle to assist a steering torque of a driver to a steering wheel by using a motor generated torque with steps comprising:
estimating a first road surface reaction torque from a steering torque,
estimating a second road surface reaction torque from a steering angle,
computing a first auxiliary return torque signal from said first road surface reaction torque,
computing a second auxiliary return torque signal from said second road surface reaction torque, and
controlling the assistant torque of said motor depending on said first and said second auxiliary return torque signals to let a steering wheel return to its original position.
Furthermore, the electric power steering control method further comprising a step of weighting to said first and said second auxiliary return torque signals for use in controlling said assistant torque of said motor.
Furthermore, the electric power steering control method further steps comprising:
judging a road surface condition from said first and said second road surface reaction torques, and
compensating a weight coefficient for weighting according to the judged result.
As described above, the power steering controller and a control method according to the present invention has the following features.
A suitable assistant torque of the motor for assisting the steering torque of a driver is generated under various driving conditions as the assistant torque of the motor is controlled into the direction for the steering wheel to return to its original position, wherein the assistant torque of the motor is obtained from the road surface reaction torque or the road surface condition.
Therefore, a driver is always able to run the automotive vehicle safely in handling the steering wheel in any driving and road conditions.